Summary "NodeVM" blocks several dangerous Node.js builtins such as "module", "worker_threads", "cluster", "vm", "repl", and "inspector". However, the denylist misses "process" and "inspector/promises". Both can be used from sandboxed code to reach host-side execution primitives. This allows sandboxed code to bypass the intended builtin restrictions and execute code in the host process. Details The dangerous builtin denylist is defined in "lib/builtin.js". This list does not include: process inspector/promises Non-denied builtins are exposed to the sandbox through: builtins.set(key, special ? special : vm => vm.readonly(hostRequire(key))); Because of this, sandboxed code can bypass the expected restrictions in two ways: 1. "require('process').getBuiltinModule('child_process')" reloads "child_process", even when "child_process" is excluded. 2. "require('inspector/promises')" exposes the Inspector protocol and can call "Runtime.evaluate" in the host process. PoC Tested on: vm2: 3.11.2 Node.js: v25.9.0 Run from the vm2 repository root: node poc/dangerous-builtin-denylist-rce.js "dangerous-builtin-denylist-rce.js" (https://github.com/user-attachments/files/27570113/dangerous-builtin-denylist-rce.js) The PoC first confirms the intended restrictions work: require("inspector"): BLOCKED require("child_process"): BLOCKED Then it bypasses them: require("process").getBuiltinModule("child_process").execFileSync(...) This spawns a host child process. It also confirms: require("inspector/promises").Session().post("Runtime.evaluate", ...) This evaluates JavaScript in the host process. <img width="858" height="766" alt="Screenshot 2026-05-10 at 11 53 33 AM" src="https://github.com/user-attachments/assets/7614aecb-5ffd-4c41-bfe8-e1fcb3b1bb59" />Impact An attacker who can run untrusted JavaScript inside "NodeVM" with affected builtin settings can escape the sandbox and execute arbitrary code in the host process. This can lead to full compromise of the application process, including reading files, writing files, spawning processes, and accessing host environment secrets. (This is not reachable with the default NodeVM configuration where require is disabled or no affected builtins are allowed. It affects applications that allow process, inspector/promises, or the wildcard "" in require.builtin.) Suggested fix Add "process" and "inspector/promises" to the dangerous builtin blocklist. Also consider blocking dangerous builtin families by prefix, for example blocking both: inspector inspector/ instead of only exact module names.